FIG. 1 is a diagram showing a front view of the door apparatus of an elevator.
A suspension jig 2 is provided at the upper end of a door panel 1. In the upper edge portion of an entrance not shown in the figure, there is provided a beam 3 whose length is arranged horizontally. The beam 3 is provided with a guide rail 4 which is arranged in a longitudinal horizontal direction. The guide rail 4 guides the horizontal movement of the suspension jig 2, i.e., the movement of the door panel 1 in opening and closing. Two pulleys 5 are pivotally fit on the beam 3 in such a manner as to be spaced from each other. An endless belt 6 is wound on both of the two pulleys 5 and is provided in a tensioned state.
A connecting jig 7 is such that one end thereof is connected to the suspension jig 2 and the other end thereof is connected to the belt 6. An electric motor 9, which is an example of a driving device, drives one of the pulleys 5 under instructions from a door controller 8. That is, when the electric motor 9 is driven, the pulleys 5 rotate and the belt 6 is driven, whereby the suspension jig 2 and door panel 1 which are connected by the connecting jig 7 to the belt 6 move in directions reverse to each other because of the movement of the belt 6 to open and close the entrance. For example, as indicated by the arrows in the FIG. 1, when the electric motor 9 rotates clockwise, the door panel 1 moves horizontally in the closing direction.
A safety shoe 10 is installed in the door panel 1. For example, in the case where the safety shoe 10 is pushed in by human contact to the door panel 1 side when the door panel 1 is driven in the closing direction, the door controller 8 sends reversal instructions to the electric motor 9 and causes the door panel 1 to be reversed in the opening direction, thereby reducing loads on obstacles (hereinafter referred to as the human body and the like) to the opening and closing of the door.
However, it is not always that the safety shoe 10 operates before contact to the door panel 1, and it seems that contact to the door panel 1 occurs before the operation of the safety shoe 10. In this case, a large contact force acts on the human body and the like.
Although there is a technique which involves reversing the door panel 1 by make a determination using a noncontact sensor, which is not shown, whether or not there is an obstacle in the moving direction of the door panel 1, this technique has the problems that it is difficult to completely eliminate blind spots of the detection region of a noncontact sensor and a large contact force may act on the human body and the like, that the cost increases due to the addition of a noncontact sensor, and so on.
As conventional techniques for reducing a contact force in the case where such a safety shoe 10 and a noncontact sensor, which is not shown, does not operate, there are techniques which involve monitoring a torque instruction value of an electric motor and reversing a door panel when a torque instruction value of not less than a prescribed limit value has continued for a prescribed time or longer (refer to Patent Literature 1, for example).
As techniques for reversing a door panel, there are techniques which involve providing a torque estimator which estimates an electric motor torque from opening and closing patterns, and detecting an overload when a difference between a torque instruction value and an estimated value has exceeded a threshold value (refer to Patent Literature 2, for example).
As techniques for reversing a door panel, in addition to those described above, there have been disclosed techniques which involve detecting an overload of an electric motor in two stages, arousing attention by use of means which issues alarms for a slight overload, and reversing the door panel for an excessive overload (refer to Patent Literature 3, for example).
Patent Literature 1: Japanese Patent Laid-Open No. 3-238286 (page 3)
Patent Literature 2: Japanese Patent Laid-Open No. 2006-182477 (page 4, FIG. 1)
Patent Literature 3: Japanese Patent Laid-Open No. 2007-254070 (pages 2 and 3, FIG. 3)